This invention has to do with vibration test bearing table apparatus of the type comprising a support block having a surface slideably supporting a test piece carrying slip plate intended to oscillate along a single predetermined test axis at a desired test frequency responsive to shaker head driving of the slip plate, and more particularly pertains to improvements in such bearing table apparatus comprising means to maintain the test piece on a single degree of freedom path coincident with the intended test axis against test piece spurious yaw, pitch and roll motions normally tended to be imparted to the test piece by the driving head.
Vibration testing is commonly carried out to ascertain the durability and response to vibratory shock of many assemblies, especially electronic assemblies, designed for severe use conditions. For the purpose of effecting such testing on a reliable and reproducible basis, bearing tables have been developed which comprise a support block usually carried on a mass and which has a highly polished surface adapted to slideably carry a slip plate. The slip plate in turn is coupled to a driving head which is vibrated at a predetermined frequency, the vibrations being carried to the slip plate by a driver bar or similar coupling. The whole function of a test protocol is to obtain reproducible results and for this purpose the operation of the shaker head, the coupling of the shaker head to the slip plate, and the slip plate carriage on the slideable surface defined by the support block are all carefully controlled.
There is, however, a problem in the perfection of the slip plate/support block slideable relation. The test piece is secured to the slip plate and the slip plate is vibrated by operation of the driving head. In practice while the force put out by the driving head is on a single axis the slip plate tends to acquire a variety of spurious cross axis motions including a front to back diving or pitch motion, a crab like or sideways motion termed yaw, and a side-to-side pitch, termed roll motion.
The result of these spurious cross axis motions is that the intended axial motion is not of the desired character and accordingly test results are adversely affected. With stringent requirements for vibration testing, it is not tolerable to have unknown cross axis forces operating which vary, in an unknown manner particularly, the test protocol.